Method loop

packages/fairygui/src/core/Timer.ts:157–159

* Execute callback repeatedly at interval * 按间隔重复执行回调 * * @param interval Interval in milliseconds | 间隔时间（毫秒） * @param caller Callback context | 回调上下文 * @param callback Callback function | 回调函数

(interval: number, caller: any, callback: Function)

     * @param callback Callback function | 回调函数
     */
    public loop(interval: number, caller: any, callback: Function): void {
        this.addCallback(interval, caller, callback, true);
    }

    /**
     * Execute callback every frame